Revert "should be BufNew,BufRead. au Filetype doesn't trigger if the filetype isn't known"

This reverts commit 53a2a55755db54bf6e37f414b47c440ef1a34f9e.

Reason: `expand('<amatch>')` for BufNew and BufRead will expand to file name.
This is not going to ever match `^\%(c\|cpp\)$` or `javascript$` unless for some
weird names.